To filter or not to filter?

For some odd reason, one of the most frequently asked questions I encounter is which, if any, filters I use on my lenses. “Especially to protect the Otuses and other rare glass”, I’m asked. I would point such questions to an article here, except I found I didn’t have one – today’s post is to rectify that oversight. The answer might surprise you somewhat…

I don’t actually think there’s a clear answer on when filters are detrimental. Remember, you are introducing an additional element into the optical formula; granted, it is supposedly planar and thin and therefore does not have excessive refractive properties, but it’s also important to remember this is dependent on ray angle: a flat filter in front of a wide angle lens with a pronounced bulge to the front element is going to result in a different angle of incidence of light compared to the naked element, which changes the optical path length slightly as you move out from the centre; all glass has a greater refractive index than air, and the more filter the light has to travel through, the more the path length changes. (This is related to the reason curved ports are preferable for underwater photography; the path difference is accentuated even further because of the refractive index of water.)

On top of this, all glass has dispersive properties, too: this is because different wavelengths of light are slowed down by different amounts as they travel through the medium. The upshot is possible additional color shifts or chromatic aberrations towards the edges, though in general it has to be a pretty thick, poor quality filter and a very wide lens before this becomes a serious issue. That said, with today’s increasing pixel density, the threshold beyond which such effects become visible is lower.

An excellent quality filter will not visibly affect anything up to a good lens; this is because losses in the lens are likely to outweigh that of the filter (i.e. 1% degradation on 30% degradation is negligible). A bad filter on a good lens will likely be the other way around: 15% degradation from the filter on top of 5% degradation from the lens. There are several ways in which a filter can go bad: uneven glass thickness; too thick glass; glass with uneven spectral transmission (obviously not applicable to color filters) leading to color shifts; poor or no coatings leading to high internal reflections; no matting on the filter ring leading to further reflections – and of course the age old favourite, dirt. It doesn’t help that some lenses seem to have a very small filter size relative to their angle of view – this further compounds corner issues by potentially introducing vignetting.

By contrast, a good filter has minimal impact on light transmission: a really good filter (Zeiss T* UV filters, for instance) will appear to be completely invisible when held up to the light. It’s tougher to assess polarisers and ND filters, because all introduce a color cast to some degree as they attenuate light; longer wavelengths possess less energy and are always the first to go, leading to a cool or magenta cast to most of these products. A further coating to correct color is therefore required; I admit given the cost of these things, I prefer to make the color adjustment afterwards in postprocessing rather than buy expensive filters at random.

In the pre-digital days, filters were necessary because there was no easy way to replicate the effects afterwards. You had to use a red filter at the time of capture to darken blue skies in B&W images; you had to use color correction filters for daylight balanced film under heavily tungsten light, gels on your flashes and the like. Polarizers were used to increase contrast and cut reflection, and ND filters to extend exposure times. Landscape photographers carried massive filter libraries to tone, tint and balance exposure to their satisfaction.

With the current state of postprocessing, we no longer need a lot of these:

Color filters. Toning is easily accomplished in postprocessing, and white balance can be set at capture or in post (providing individual channels are not overexposed). Even for monochrome conversion, it’s very easy to use the channel mixer to knock down the luminance components of individual wavelengths in a very targeted manner, and without losing transmission as you would with a red or orange filter (up to 1.5 stops overall). The one exception to this is if you shoot a monochrome-only camera; the sensor in that will be luminance sensitive only and have no color information to remix afterwards – you are back to using filters.

Gradient filters. We can now just drag gradients in ACR/PS, and have them affect more than exposure and color; instead, everything on the basic panel (and some others, like sharpening, clarity and dehaze) are now available, too.

Neutral density (ND) filters are debatable, too: if you stack and average enough sequential long exposures, you can reach the same approximate result as an ND. Auto-alignment can take care of any possible movement issues; though this remains the one snag – and preserving continuous motion without gaps, though for stochastic subjects like waterfalls and clouds etc. this is less critical. A further advantage of not having an ND filter is avoiding potential color shifts, though I admit I continue to use ND filters personally.

However, there are still few things that cannot be replicated digitally:

UV and IR filtration – early generations of cameras had poor filtration over the sensor leading to the blue channel being susceptible to blowout by UV sources such as violet flowers, or the red channel being oversensitive especially under incandescent light or blacks experiencing red/magenta shifts. Our eyes don’t see outside the visible spectrum and attenuate accordingly to result in our ‘normal’ perception of color; subsequent improvements to the filter pack to more closely match this tonal response have resulted in much more accurate color. However, what I have noticed on some recent cameras is that the AF modules can be fooled by very warm light sources – the PDAF module sits before the filter pack in front of the sensor and can be influenced to focus on the wrong thing. Using a IR (and sometimes UV) cut filter can help in these situations. The Heliopans work best, but boy do you pay the price…

Obviously, environmental protection for the front element.

Most of the time, I do not use any filters. Front elements are tougher than you think; on top of that, you can always use the hood for impact protection – the number of times a hood has cracked to save me is quite a few. Filter glass is no stronger than front element glass – and probably weaker in many cases even if it’s the same chemical formula – it’s simply thinner. However, for every tale of ‘my lens was saved by the filter’ – I’ve seen an equal number where a cracked filter resulted in bits of very abrasive glass scrubbing the front element and necessitating in replacement anyway; at very least, the coatings are going to be toast. And now instead of replacing just the hood or front element, you’ve paid for the filter, too. The one exception to this is when you’re shooting in unfriendly environments – sand, water, mud, sea spray; I’d rather my filter get sandblasted than my front element.

The main reason I avoid filters (except for the usage cases above) is because I often do see a difference. Aside from the obvious scenario of shooting into light sources and seeing significant ghosting, the problem is if you’re using an Otus – anything you put on the front of it, Zeiss’ own filters included, will visibly degrade contrast. It seems that the planar filters introduce reflections that simply weren’t an issue previously with the concave front elements of the 55 and 85mm Otuses. The same is generally true of other lenses with concave fronts, too: they tend to maintain higher contrast without filters; probably because there are fewer paths for internal reflection (and thus stray light, flare and reduction in contrast) to take place.

Tellingly, lenses designed to take filters – most of the superteles, and some superwides – the filter holders are placed internally as a drop-in or at the rear of the lens, and designed in as part of the optical formula to avoid light coming from odd angles of incidence. This is also because a 150+mm filter front filter for a 400/2.8 would be prohibitively expensive and unwieldy, though many of those lenses have an easily replaceable screw-in front meniscus element that’s both concave and uniform thickness. Even so, this too is part of the optical formula.

I find the most cost effective approach is to buy your key ‘effect’ filters (circular polariser, 10 stop ND, 2-10 or 1-5 stop variable ND) in the thread size of your largest lens and then invest in step up/down rings, but spend money buying the best filter available instead. I avoid the warming/cooling/tinting combination filters because it becomes very difficult to accurately correct color afterwards; you have to like ‘the look’ they provide and get the white balance correct at capture. I’ve also seen a couple of my students use magnetic filter holders (threaded part attaches to lens; threaded part to filter; they stick together with magnets) for quick changes; whilst it seems like a sensible solution, the problem is it adds significant thickness to the filter stack – which may cause vignetting. Other filters like UV protection or UVIR cut can be in a range of sizes that cover your typical lens load – simply because having to swap them out in the field defeats the point of environmental protection. On top of that, the mounting rings are not cheap, and you also have to use special magnetic caps since the clip on type will no longer have any threads to grip. Bottom line: make sure the filter actually does something that you can’t replicate afterwards, and don’t make the mistake of saving a few bucks and putting a bad bit of optics in front of one you’ve paid good money for. MT

Here are my filter recommendations based on my own personal use (with links):

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Debating between B&W or Zeiss polarizer for Zeiss Milvus 21mm? Zeiss is $75 more than the B&W ($200 vs 125). Would either filter or both change the rendering of the Zeiss lens? Which one would you recommend and why? Thanks.

Yeah, I don’t understand all the people who think filter protection is just for dropping or knocking the lens into something. That’s the least of what I am worried about. I get junk on my filter all the time. I have to clean my filters fairly frequently. I almost never clean my lens front elements.

Late entry. I put good quality filters on all my lenses. If I’m inside or outside with no/little wind, I take them off along with the lens cap and place them in a soft pouch. The lens hood does provide adequate protection. Outside in windy conditions I leave them on. Yes I know front elements on good quality lenses are strong. But so are car windshields. And after driving on ONE snowy day where sand has been used on the roads, EVERY windshield has countless divots in it; talk about flare! Blowing sand/dirt is very abrasive; that’s why they put it on icy roads. I can live with a little filter flare. Moreover, the loss of image quality is so small with a good filter on a good lens that it won’t be noticed on a standard sized print. Getting a front element repaired will be expensive, or maybe impossible with an older lens.

Off topic, but I was wondering whether or not you could share with us your method of cleaning your camera’s sensors. Sorry if this has been answered elsewhere, but I couldn’t find it. Love your blog and your intellect. Best regards Gregg

It hasn’t. I rarely have to wet clean anything anymore – those cameras with sensor shakers require a puff from the blower once every few weeks, and some not at all (Olympus). The Hasselblads are the most dusty because of the interchangeable backs, and even then they require only a blower puff once a day under heavy shooting. If I had to wet clean one, it’s easy because the sensor is completely exposed.

Thanks Ming. I too use wet cleaning, but only as a very last option, and actually have never cleaned my current Canon dslr which is now 4 years old. Have you had any experience with the “Pentax imagesensor cleaning kit”, which is the sticky rubber blob on the end of a stick. Many thanks once again. Great blog!!

One reason to use a UV filter in front of the lens is that in tropical climates when you leave your air conditioned hotel room (or home), and go out to the 90% humidity, condensation immediately forms on all exposed surfaces including the front lens element. Hood does not help. It can take 15-30minutes of warming up before it disappears. I prefer to wipe the filter a few times when I see a picture instead of the front element as this happens every day and often several times in the morning. Important to also plan ahead what lens to use as removing a cold lens first thing in the morning will really cause havoc with condensation on the mirror, rear of the lens etc.
In cold climates it is the opposite. When you come in from the freezing weather, condensation is a problem but usually less so as you have taken your pictures and can leave the camera on the table. Some suggest putting it in a plastic bag until it warms up, But that does not help when you are out in the morning at best light and something interesting happens in front of you.

You can also get condensation between front element and filter – then you’ll have to clean both sides. Happened to me before 🙂

And yes, don’t change lenses until everything has warmed up. Early morning birding many years ago with a 500/4 was frustrating until I drove to the location with the A/C off – better the humans suffer humidity than the cameras…

Protection filters are one of those questions a lot of beginners wonder about, so it’s good to have a detailed answer! Here’s some of my experience with filters that may be helpful, too.

A tip that may help others for getting stuck filters off: forget the wrenches, they’re fiddly and don’t work very well. Use the underside of a neoprene mouse pad or maybe a wetsuit. Use whatever is the grippy part that you don’t roll your mouse one, and press the front of the lens onto the mat and rotate counterclockwise. Make sure the front element won’t rub against the mat though, but you don’t need to press down too hard. This method’s gotten off some really stubborn filters, especially on the chrome-ringed Zeiss classics (ZF/ZE) that can have a tenacious grip, or strangely no grip at all.

I also like to use filters that use brass rings instead of aluminum. They seem to be easier to remove. For my step-up rings, that generally means Heliopan or Sensei. I’ve also done the 77mm standardization, and it’s very helpful, especially for eliminating purchases of lenses which have bigger filter sizes!

I’m one of Ming’s students who’s using the Xume magnetic system. In general, it’s a very useful, convenient system, and I’ve only noticed vignetting on extreme shifts of the Nikkor 24 PC-E, but I’ve also not tried using it on anything wider than 24mm. The filter adapters and rings are very thin, and made of aluminum, and you’ll need the neoprene pad to get them off.

I also have a Lee system for the grad filters. I do find them useful because I’d rather put all the information into the sweet part of the sensor’s response and then pull it apart again in post. Ming is right in that it’s a bulky system to carry around, and it’s rather expensive too: I don’t like to travel with it because of its size. It’s also a little disconcerting to stick a bit of plastic with finger smudges on the edges in front of your lens: the grads are mostly plastic. Their ND filters are glass. I discovered this weekend that they’re great for overcast conditions because the sky is still very bright, but the ground is darker than normal because there’s less light falling on it. And if you shoot video, grads are an interesting way to create a lighting effect, especially when you use two together.

I only have a 2-stop hard grad, and a 6-stop ND for the Lee. If I were to fill out the rest of the system with a 10-stop ND and a polarizer, it’d be about $500 more.

The mouse pad trick is extremely useful – it’s saved me a couple of times. Got to now figure out how to remove stacked filters. Why the filter makers don’t do a pair of opposing lugs on their filters so we can twist them off easily is beyond me…

That would be a good idea! Or maybe little holes or indentations in the ring on opposite sides like the screw-in rings used to attach large format lenses to lens boards might work too allowing you to use optical spanner wrenches.

I had a 72-77 step-up ring that got too cozy with a Lee 77mm wide angle adapter ring, and the step-up ring is almost flush with the surface of the ring, but the mousepad saved the day again. Since there was no glass, I could press really hard into the pad to get a good grip on it.

Maybe a mousepad with a hole cut in it to avoid touching the glass might work? Or two pads, both with holes cut, with each pad on either side to grip the filter ring?

Pop in to your nearest kitchen shop and buy a jar opener – it’s a 6″ circle of grippy rubber (grippier than neoprene) and easily packable in your camera bag. Works like a dream. Also usable for opening screw-on watch backs – and if you’re old and decrepit like me, you can even use it for opening jars… 🙂

I’m of the filter for protection school. Recently I tripped on a kerb and the lenshood took the brunt of the fall. The filter on the lens shattered and made a small scratch on the front element. I would have been better without the filter.

This is my only incident in over 40 years of photography so in my case I could have saved a small fortune in filter costs over the years.

I wonder how many reporting on this issue actually can trace a photographic history going back to film and will know that lenses from the 50’s and 60’s were made from relatively soft optical glasses and the coatings were nowhere near as robust as those of today. As you, I go back a few decades to when I started in this hobby, 1959 in fact, and can report first hand accounts of how easy it was to scratch a lens when trying to clean it. So this filter issue for people like me is a hangover from years ago when it made far more sense to protect the lens from the elements, NOT physical damage.

Yes, that happened to me several years ago, a UV protective filter on my 105mm/2.8 AF Micro Nikkor shattered when I tripped. I had to have the front element replaced. About the same time I noticed the UV filter harmed corner performance on the 20mm/2.8 AF Nikkor and swore off using filters except polarizers or colored filters for B&W film.

Last year I accidentally dropped my Leica M-P and 35mm/1.4 Zeiss ZM lens, which had a Zeiss polarizer on the front. The filter cracked, and a shard of glass came loose, but didn’t meet the front element, fortunately. I felt like a lucky guy.

Hi Ming,
this must be the article on filters that is closest to my personal opinion;)
I agree with most of what you said but I think you may have overlooked some points. It was already mentioned that you may need a filter for complete weather sealing. The Canon 17-40 is one such case. If you read on the forums, more often than not the same people who herald the L lenses and their “professional, weather-sealing design” will whole-heartedly condemn filters. Makes no sense.
I don’t agree that we don’t need graduated filters anymore. They can be a tremendous help if conditions are highly dynamic and they often are. Sure, you can do DRI or maybe your camera has excellent dynamic range but sometimes DRI isn’t feasible and your camera may be a bit lacking in DR. In that case, filters really are your only option.
What is more important, I think is that there is a certain way of working connected to using NDs and ND Grads. In many occasions, you can easily replicate the result in Photoshop. But I know I wouldn’t want to do that. When it comes to things I can achieve in camera as well as in post, I will always choose to do it in camera. Kind of like your stance on cropping. Sure, there isn’t really any right or wrong here but I tremendously enjoy coming home with an image that I can process in about 15 minutes as opposed to some “raw material” which I will turn into an image in post. There isn’t really anything wrong with the latter but I vastly prefer the first. Using filters, especially grads, allows me to do that. I think that difference in experience can really make a difference for some people.
Cheers

At least some variable ND filters produce a visibly darker “X” shape in the image at the darker end of their range. Is that something you experience with your recommended filters and how far can you go before you see it? Thanks!

I’ve been shooting for many many years and have never used a protective filter. On 2 occasions however, my lens hood saved one of my lenses from destruction. The only time I’ve not used a lens hood is with certain very wide lenses where a hood would obstruct, and the only filter I ever use is a circular polarizer which occasionally comes in handy with it’s unique qualities.

I can’t tell you the number of times I’ve had a filter or lens damaged by such a jury-rigged device. This is the sort of pseudo-scientific mumbo-jumbo that I can’t believe people take seriously. I suppose there must be something on the internet where someone actually shoots bullets at a filter/lens combo and is surprised that they don’t survive. Give me strength!

Sure, as a scientist I can tell that the methodology is not flawless. But it still beats all the hearsay and anecdotal evidence that is usually cited in discussions on this topic. The bullet analogy is not very apt. The main point is that a lot of things can damage or destroy a filter, but would do little or no damage to the lens. In the end, everyone can make their own choices, filter or no filter, I don’t care much.

I’ve only knocked a lens once and it was the hood that saved the lens not the filter. So I don’t think filters are necessary for protection. And except for special purposes I would prefer not to use filters because it’s an extra layer of glass for the light to go through. But, Korea is a dusty, dusty country, especially when the Yellow Sands come from China. Cars are dirtier after rain falls. For that reason I always keep a UV filter on my lenses for dust protection. Even with a filter a few specks of dust and dirt find their way onto the front element.

An interesting, and personal, view regarding the advocacy, or not, of using filters. You point out the need for filters being greater with film for the very reasons to which you allude, and I wholeheartedly agree. I still have my Gossen colour meter and set of Rollei colour correction filters and what fun, or pain, it was using, along with the usual gamut of coloured, or “contrast” filters to give them their proper name, for b/w film use.

Being “old school” I always kept a UV filter on my lenses and with film I can’t honestly say I noticed any detriment. Perhaps this is an advantage of the medium. I still carry this practice over to my digital camera lenses as a matter of course, although I have wondered what this could be doing to the images as sensors increase in resolution.

I believe it is too easy to argue that any glass in front of one’s lenses has to be detrimental; after all it is difficult to refute the argument in principle, isn’t it? In reality, it can do, but quite often one won’t really notice that much difference, if at all, unless one is using top jolly lenses and high res sensors AND you can see the difference. I suppose the point I would make is that if you are more content using a protective filter, then do. If you obsess about what it may or may not be doing to an image, then don’t.

But if you are going to use a filter, then get a decent one, and expensive doesn’t necessarily mean get you the best. This topic is very subjective and a good bit of science won’t go amiss to help you decide which filter to buy. Here is an article and which, although it is now getting on for seven years old, is quite illuminating on the subject and could save you money.

One little point: ‘correction filters on lenses to change ambient to match flash’. Then both the ambient and the flash sources are being filtered, and the imbalance persists. So it’s either gels on flash or gels on ambient (when the ‘ambient’ is, for instance, a small interior light). Clearly a lens filter remains an option to adjust everything together, if this rather than in-camera or post-processing is preferred).

Incidentally, I’ve recently been using a Sekonic C-700 spectrometer and colour-temperature meter – quite shocking to see the spectrum from compact fluorescent lamps, but encouraging that the better LED sources now are much more nearly continuous – still not a patch on the sun, or an incandescent lamp, or a conventional flash, though!

I photograph outdoors a lot and often in inclement weather, so I pretty much have a protector filter mounted all the time. They are also useful when photographing kids up close, they’ve saved my front element from smudges plenty of times when a toddler suddenly reaches for the lens.

Other than that, I only use CPL and ND filters. I’m currently using Breakthrough products, got their 10-stop ND and CPL both in 77mm along with step-down rings for all my lenses. Their filters are quite color neutral, only requiring very little color correction, and they don’t noticeably degrade sharpness on a 16mpx m4/3 body. They use high quality materials and have excellent construction. They are not exactly cheap, though, same ballpark with other high quality manufacturers.

I stumbled upon them by accident in Kickstarter when they were raising funds for their X4 CPL project. There wasn’t many reviews about their stuff online so I took a leap of faith and backed their project. I’ve been meaning to make a short write-up on their filters in your Flickr group, but haven’t gotten around to it yet. I will need to take some good comparison shots with and without the filters so everyone can see for themselves how they change the image properties. Starting in June I’m having 10 weeks off from work and this is one thing on my to-do list.

Hi, I totally Agree with your way of thinking.
I don’t use filters. But I always use lens hood.
I break this rule when I bought Tamron 60B 300 2.8.As hood is huge, and front lens is superbig and super exposed to scrath, I bought protector filter :).
And thanks for idea of stacking for long exposure in day time.

Interesting point of view as always Ming. Apart the ND filters I use for those rare long exposures (I’m not patient enough to “simulate” it in post production), and a couple of filters I use to cut out (or improve) reflections, I gave a try to the new Hoya Fusion serie, on the Leica Q. I bought the antistatic version and I must admit that it works: less dust on the filter and it comes away easier too.
I admit though that with some some incidental light, like that from strobes in a dark studio for example, the risk of flares is quite high and I remove it.
Thanks for the post!

Interesting. Thanks for the explanation!. I’ve been using B+W circular polarizers–the weather resistant kind, and they’ve come out with new versions saying that they’re much more efficient, allowing better transmission of light.

I still have yet to buy a neutral density filter because I’m not making films with my video clips, and the only reason I see why people use them on still photography is for tricks.

I have one filter nearly permanently mounted, and that is on the filter adapter for my Coolpix A. It’s a B+W UV 46mm filter. The idea is that this minimizes lens cleaning needs. I do sometimes change that for a Polarizer.

There is a bit of grey area in some lenses where a filter is necessary to complete its weather-sealing though, notably a couple of Canon lenses such as the 16-35L and 50L.

And then there are certain “hostile environments” where a filter actually does more harm that good. I remember someone doing a test where a lens hit by a pain ball (sic) came out worse with filter than without. 😀

I think only the manufacturers can answer that. Wouldn’t make sense to need the filter if the lens doesn’t physically change when focusing or zooming though, and even if it does the moving portion can be sealed.

I personally have never used filters on any of my lenses for many years. I did at one point when I seriously got into photography about 7 years ago, then when street shooting at night, I noticed so many flares / glares / haze in my images? and I found out it was from the filter I was using, I forget the brand at the time, so when I took it off, everything was better. When my friends complain of additional flares, I tell them to try and take their filter off and see if it helps, and 9 times out of 10 they are surprised, they were using cheap filters by the way.

Sometimes filters can cause more damage than protect, my friend dropped his Nikon 24-70 lens on the ground, while on vacation in Japan, his filter cracked in many places, but his filter ring was bent, he couldn’t take off the filter because of the bent metal filter ring, so he couldn’t shoot, visibility was bad from the cracked filter in place. I told him to crack it some more to take out the cracked filter glass so he could shoot while still on vacation or visit a Nikon repair center in Japan to have them repair it.

Yes, the more expensive and better brand filters won’t impact Image Quality, and some like it because it is protection from ocean spray or dirt and dust. Its just that most don’t want to spend over $80 for a filter and will get cheap ones, resulting in bad image quality.

For the past 40+ years I have always used uv/clear filters to “protect” the lens element. Only recently I had my first accident, I tripped on a kerb, and the rim of the filter took the main brunt of the impact. Guess what the filter shattered and left a mark on the lens. I could have saved a tidy sum in filter costs over the years.

Timely article on a somewhat controversial subject. I always preferred using hoods and lens caps for front element protection, although I suppose the shards from a broken lens cap can do as much damage as shattered glass from a smashed filter.

Thanks a zillion, Ming – that comes across to me as the most thorough, thoughtful and comprehensive article I’ve ever seen on this topic. Which says a great deal – because for perhaps the majority of photographers out there, this is a very worrying issue and one on which practically everyone seeks & wants guidance from someone better informed than they are.

I like your suggestion of the large filter (high quality) and step-down rings, although of course that would also mean using the larger lens hood.

There is one point I’ve come across, which may help some people make their decision. With digital cams, the use of a UV filter is less important than it might have been in the days of film. The actual digital process these days apparently achieves the same or similar results, without any need for a UV filter, at all.